Desirable objectives of an amination process are to increase the amount of linear amination products and decrease the formation of cyclic amination products. See for example the U.S. Pat. Nos. 2,365,721 and 3,766,184 and EP-A-146 508, EP-A-254 335, EP-A-729 785 and EP-A-737 669.
Another desired objective of an amination process is to reduce the amounts of by-products which may cause discolouration of the polyamines themselves or, at a later stage, cause discolouration when the polyamines are used as intermediates or in compositions. A number of methods for reducing the colour has been suggested. For example, the U.S. Pat. No. 3,723,529 suggests treatment with activated carbon and the U.S. Pat. No. 4,347,381, treatment with a bleaching agent. EP-A-262 562 discloses a method for the reduction in the colour by contacting the coloured polyamines at elevated temperature and pressure with a catalytically effective amount of a hydrogenation catalyst in the presence of a hydrogen containing atmosphere. However, although all of these methods do result in a reduction in colour the post-treatment is costly and does not prevent the occurrence of discolouration.
The purpose of the present invention is to increase the selectivity of the linear aminated products and at the same time prevent the formation of discolouring by-products or by-products which later may be the future sources of discolouration, for example when neutralizing the aminated products with an acid. Furthermore, the solution to the above-mentioned challenges should be uncomplicated and should not lead to other problems.